Current transmission schemes for infrared remote controls include transmitting a signal with a carrier frequency and on/off keying for data transmission. The on/off keyed data is usually transmitted in either Biphase, Manchester, Pulse Position, or Pulse Width form.
Typically, infrared transmission schemes such as Infrared Remote Controls (IRC) have a carrier frequency falling within the range of 30-60 KHz. A disadvantage associated with IRC is that different remote control devices interfere with each other during simultaneous transmission. Thus, only one device can transmit at a time. This is particularly disadvantageous where it is desirable to control multiple remote devices simultaneously such as in a network configuration.
Another disadvantage associated with IRC is that the data rates are limited up to 4 Kbits per second. For many new generation input devices such as digitizers and touchpads where character recognition is desired, higher data rates are needed.
A further disadvantage associated with IRC results from the light emitting diode (LED) pulse switching transients. On/off keying leads to spectral impurity and associated broadband noises which limit the ability of multiple devices to transmit simultaneously.
A recently proposed technology called Consumer Infrared (CIR) also uses on/off keying. CIR is essentially a faster version of IRC but uses a 1.6 MHz carrier. The data rate for CIR is much higher than IRC. For instance, the data rate for CIR is 50 Kbits per second using Manchester encoding. However, CIR suffers from many of the same disadvantages suffered by IRC.
For instance, it is impossible to control multiple devices simultaneously with CIR. CIR possesses an unacceptable on/off keying spectral impurity similar to that of IRC. Furthermore, CIR has no provision for broadcasting live real time audio. Additionally, CIR supports a maximum of three communication channels. Market convergence requires more bandwidth than can be provided by these existing channels.
What is needed is an infrared communications scheme where multiple channels at separate carrier frequencies can communicate without disrupting each other.